In a manufacturing process of a semiconductor device or a flat panel display (FPD), a plasma is widely used in a process such as etching, deposition, oxidation, sputtering or the like since it has a good reactivity with a processing gas at a relatively low temperature. In such plasma process, the plasma is mostly generated by a high frequency discharge in the megahertz range. Specifically, the plasma generated by the high frequency discharge is classified into a capacitively coupled plasma and an inductively coupled plasma.
Typically, an inductively coupled plasma processing apparatus includes a processing chamber, at least a portion of wall (e.g., a ceiling portion) of which is formed of a dielectric window; and a coil-shaped RF antenna provided outside the dielectric window, and a high frequency power is supplied to the RF antenna. The processing chamber serves as a vacuum chamber capable of being depressurized, and a target substrate (e.g., a semiconductor wafer, a glass substrate or the like) to be processed is provided at a central portion of the chamber. Further, a processing gas is introduced into a processing space between the dielectric window and the substrate. As a high frequency current flows though the RF antenna, an AC magnetic field is generated around the RF antenna, wherein the magnetic force lines of the AC magnetic field travel through the dielectric window and the processing space in the chamber. The temporal alteration of the generated AC magnetic field causes an electric field to be induced azimuthally. Moreover, electrons azimuthally accelerated by the induced electric field collide with molecules or atoms of the processing gas, to thereby ionize the processing gas and generate a plasma in a doughnut shape.
By increasing the size of the processing space in the chamber, the plasma is efficiently diffused in all directions (especially, in the radical direction), thereby making the density of the plasma on the substrate uniform. However, the uniformity of the plasma density on the substrate that is obtained by merely using a typical RF antenna is generally insufficient for the plasma process. Accordingly, in the plasma process, it becomes one of the most important factors to improve the uniformity of the plasma density on the substrate, since it determines the uniformity and the reproducibility of the plasma process itself and, furthermore, the manufacturing production yield.
In the inductively coupled plasma processing apparatus, the plasma density distribution characteristics (profile) in the doughnut-shaped plasma generated near the dielectric window in the chamber are important, and the profile of the plasma density distribution affects the uniformity of the plasma density distribution obtained on the substrate after diffusion.
As for techniques for improving uniformity of radial density distribution of a plasma, there have been suggested several methods for dividing an RF antenna into a central and a peripheral spiral coil segment in a radial direction. Such RF antenna division methods include a first method for supplying a high frequency power to each of the spiral coil segments (e.g., Patent Document 1), a second method for controlling a distribution ratio of a high frequency power distributed from a single high frequency power supply to antennas/segments by varying impedances of the spiral coil segments in an additional circuit such as a capacitor or the like (e.g., Patent Document 2), a third method for connecting a central and a peripheral spiral coil segment to a single high frequency power supply in series and connecting a short-circuit switch or a variable capacitor to the central spiral coil segment in parallel (e.g., Patent Document 3), and the like.